1. Field of The Invention
This invention relates to communication systems and, more particularly, OFDM (Orthogonal Frequency Division Multiplexing) modulation schemes which are suitable to provide a wide range of information transfer rates in a wide range of physical environments.
2. Description of Related Art
OFDM is a block-oriented modulation scheme that maps N data symbols into N orthogonal carriers separated by a distance of 1/T, where T is the block period. As such, multi-carrier transmission systems use OFDM modulation to send data bits in parallel over multiple, adjacent carriers (also called tones or bins). An important advantage of multi-carrier transmission is that inter-symbol interference due to signal dispersion (or delay spread) in the transmission channel can be reduced or even eliminated by inserting a guard time interval between the transmission of subsequent symbols, thus avoiding an equalizer as required in single carrier systems. This gives OFDM an important advantage over single carrier modulation schemes. The guard time allows delayed copies of each symbol, arriving at the receiver after the intended signal, to die out before the succeeding symbol is received. OFDM's attractiveness stems from its ability to overcome the adverse effects of multi-channel transmission without the need for equalization. A need exists for a flexible OFDM system which provides the advantages of OFDM to a variety of communication environments.